1. Field of the Invention
The present invention relates to a liquid fuel injection system for injecting atomized liquid fuel into a liquid injection space; specifically, an intake path of an internal combustion engine.
2. Description of the Related Art
Conventionally known liquid fuel injection systems include a fuel injection system for use in an internal combustion engine. The fuel injection system is a so-called electrically controlled fuel injection system, which is in wide use and includes a solenoid-operated injection valve and a pressure pump for pressurizing liquid fuel. In the electrically controlled fuel injection system, fuel is pressurized by means of the pressure pump and injected from an injection portion of the solenoid-operated injection valve. As a result, liquid droplets of injected fuel have a relatively large size of at least about 100 μm and are not of uniform size, whereby a large amount of fuel remains unburnt during combustion, leading to increased emission of undesirable exhaust gas.
Meanwhile, Japanese Patent Application Laid-Open (kokai) No. S54-90416 discloses a liquid droplet ejection system. In the liquid droplet ejection system, a piezoelectric/electrostrictive element is operated so as to pressurize liquid contained in a liquid feed path, thereby ejecting the liquid from an outlet in the form of fine droplets. Such a system utilizes the principle of an ink jet apparatus disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. H06-40030 and can eject finer liquid droplets (liquid droplets of fuel) of uniform size as compared with the above-mentioned electrically controlled fuel injection system, thereby realizing excellent liquid (fuel) atomization performance.
A liquid ejection system that utilizes the principle of an ink jet apparatus can eject fine liquid droplets as expected when used in a relatively steady atmosphere with little variation in temperature, pressure and the like (e.g., in an office, a classroom, or a like indoor space). However, the liquid ejection system usually fails to realize sufficient atomization performance when used under wildly fluctuating atmospheric conditions as found in the case of an internal combustion engine, which involves fluctuating operating conditions. Under the present circumstances, there has not been provided a liquid injection system that utilizes the principle of an ink jet apparatus and can inject sufficiently atomized liquid even when used in a mechanical apparatus involving wildly fluctuating atmospheric conditions as in the case of an internal combustion engine.
Additionally, even when sufficiently atomized liquid fuel is injected into the intake path of an internal combustion engine, if air flows at high velocity or turbulently in the intake path, liquid droplets of fuel collide and grow into larger droplets. The thus-grown liquid droplets may adhere to a wall or surface which forms the intake path (e.g., the wall surface of an intake port or a back surface of an intake valve); as a result, fuel may fail to be injected into a cylinder in a well-atomized condition.